fix double extrahead in docs

Author: topi314

docs/overrides/main.html

@@ -1,13 +1,9 @@
 {%- block extrahead -%}
-    <meta name="darkreader" content="">
+<meta name="darkreader-lock">
 {%- endblock -%}
 
 {% extends "base.html" %}
 
-{% block extrahead %}
-<meta name="darkreader-lock">
-{% endblock %}
-
 {% block announce %}
 The Lavalink docs are currently a work in progress. You can give us feedback on <a href="https://github.com/lavalink-devs/Lavalink">GitHub</a>
 {% endblock %}